Formation of conductive rugged silicon

ABSTRACT

The present invention provides methods of forming in situ doped rugged silicon and semiconductor devices incorporating conductive rugged silicon. In one aspect, the methods involve forming a layer of amorphous silicon on a substrate at a substantially constant deposition temperature; and converting the layer of amorphous silicon into hemispherical grain silicon by subjecting the layer of amorphous silicon to substantially the deposition temperature while varying pressure.

This is a continuation of application Ser. No. 09/503,572, Feb. 14,2000, U.S. Pat. No. 6,509,229, which is a continuation of applicationSer. No. 08/808,235 filed Feb. 28, 1997 (issued as U.S. Pat. No.6,069,053 on May 30, 2000), both of which are incorporated herein byreference in their entireties.

FIELD OF THE INVENTION

The present invention relates to the field of semiconductormanufacturing. More particularly, the present invention provides methodsof obtaining conductive rugged silicon.

BACKGROUND OF THE INVENTION

Electrically conductive rugged silicon surfaces are useful in themanufacturing of dynamic semiconductor storage devices requiring storagenode capacitor cell plates large enough to maintain adequate charge,i.e., capacitance, in the face of parasitic capacitances and noise thatmay be present during operation of a circuit including the storagedevices. Maintaining storage node capacitance is especially importantdue to the continuing increases in Dynamic Random Access Memory (DRAM)array density.

Such DRAM devices, among others, rely on capacitance stored between twoconductors separated by a layer of dielectric material. One method ofincreasing the capacitance of a capacitor formed using conductivepolysilicon layers is to increase the surface area of the conductors.Using conductive rugged silicon for the first conductor is one method ofincreasing the surface area of the conductors because thelater-deposited dielectric layer and second conductor will typicallyconform to the surface of the first deposited conductor.

Hemispherical grain silicon (commonly referred to as HSG silicon) is oneexample of a silicon layer with a rugged surface, i.e., a surface thatis not smooth. Hemispherical grain silicon can be obtained by a numberof methods including Low Pressure Chemical Vapor Deposition (LPCVD) atconditions resulting in a layer of roughened polysilicon. Another methodincludes depositing a layer of amorphous silicon, followed by hightemperature seeding and annealing to cause the formation of HSG silicon.

The silicon layers to be converted into HSG silicon or deposited as HSGsilicon are not, however, typically in situ doped during depositionbecause in situ doping of the amorphous silicon can result incrystallites within the amorphous silicon layer. As a result, additionalsteps, such as seeding and/or annealing are required to reliablytransform the in situ doped, generally amorphous silicon into ruggedhemispherical grain silicon. Those additional steps increase cost anddecrease throughput.

SUMMARY OF THE INVENTION

The present invention provides methods of forming in situ conductivelydoped rugged silicon. In one aspect, the present invention provides amethod including steps of forming a layer of doped amorphous silicon ona substrate at a substantially constant deposition temperature; andconverting the amorphous silicon layer into hemispherical grain siliconby annealing the amorphous silicon layer at substantially the depositiontemperature while varying pressure.

In another aspect, the present invention provides a method of forminghemispherical grain silicon including steps of forming a layer of dopedamorphous silicon on a substrate at a substantially constant depositiontemperature of about 565 to about 575° C.; and converting the amorphoussilicon layer into hemispherical grain silicon by annealing theamorphous silicon layer at substantially the deposition temperaturewhile varying pressure.

In another aspect, the present invention provides a method of forminghemispherical grain silicon including steps of forming a layer of insitu doped amorphous silicon on a substrate at a substantially constantdeposition temperature; forming a layer of undoped amorphous silicon onthe doped amorphous silicon layer at the deposition temperature; andconverting the doped and undoped amorphous silicon layers intohemispherical grain silicon by annealing the silicon layers atsubstantially the deposition temperature while varying pressure.

In another aspect, the present invention provides a method of forminghemispherical grain silicon including steps of forming a layer of dopedamorphous silicon on a substrate at a substantially constant depositiontemperature of about 565 to about 575° C.; forming a layer of undopedamorphous silicon on the doped amorphous silicon layer at the depositiontemperature; and converting the doped and undoped amorphous siliconlayers into hemispherical grain silicon by annealing the silicon layersat substantially the deposition temperature while varying pressure.

In another aspect, the present invention provides a method of forminghemispherical grain silicon including steps of forming a discontinuousfirst layer of doped silicon on a substrate; forming a second layer ofamorphous silicon on the first layer of doped silicon and the substratenot covered by the first layer of doped silicon; and annealing the firstand second layers.

In another aspect, the present invention provides a method of forminghemispherical grain silicon including steps of forming a discontinuousfirst layer of doped silicon on a substrate at a deposition temperatureof about 600° C. or greater, the first layer having a concentration ofdopant of about 10²⁰ atoms/cm³ or greater; forming a second layer ofamorphous silicon on the first layer of doped silicon and the substratenot covered by the first layer of doped silicon; and annealing the firstand second layers.

In another aspect, the present invention provides a method of forminghemispherical grain silicon including steps of forming a discontinuousfirst layer of doped silicon on a substrate; removing a portion of thefirst layer of doped silicon from the substrate; forming a second layerof amorphous silicon on the first layer of doped silicon and thesubstrate not covered by the first layer of doped silicon; and annealingthe first layer of doped silicon and the second layer of amorphoussilicon to form hemispherical grain silicon.

In another aspect, the present invention provides a method of forminghemispherical grain silicon including steps of forming a discontinuousfirst layer of doped silicon on a substrate at a temperature of about600° C. or above, wherein the concentration of dopant in the first layerof doped silicon is about 10²⁰ atoms/cm³ or greater; removing a portionof the first layer of doped silicon from the substrate; forming a secondlayer of doped amorphous silicon on the first layer of doped silicon andthe substrate not covered by the first layer of doped silicon; andannealing the first layer of doped silicon and the second layer of dopedamorphous silicon to form hemispherical grain silicon.

These and other features and advantages of methods according to thepresent invention are described in the detailed description of theinvention below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional schematic diagram of one layer of HSGsilicon produced according to the present invention.

FIG. 2 is a graph of deposition temperature (y-axis) as a function oftime (x-axis) in one method of providing HSG silicon according to thepresent invention.

FIG. 3 is a cross-sectional schematic diagram of one method including acap layer of undoped silicon.

FIG. 4 is a graph of pressure (y-axis) as a function of time (x-axis) inthe method of FIG. 2.

FIG. 5 is a cross-sectional schematic diagram of the formation of adiscontinuous first layer of polysilicon in one method of providing HSGsilicon according to the present invention.

FIG. 6 is a cross-sectional schematic diagram of the formation of asecond layer of amorphous silicon on the discontinuous first layerdepicted in FIG. 5.

FIG. 7 is a graph of deposition temperature (y-axis) as a function oftime (x-axis) in another method of providing HSG silicon according tothe present invention.

FIG. 8 is a cross-sectional schematic diagram of a layer of ruggedsilicon formed using a first discontinuous layer of silicon and a secondconformal layer of silicon.

FIG. 9 is a cross-sectional schematic diagram of a capacitor including alayer of conductive rugged silicon formed using methods according to thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention comprises methods of providing conductive ruggedsilicon from an in situ doped layer of amorphous silicon. As discussedabove, rugged silicon, including hemispherical grain silicon, isparticularly useful in the manufacture of DRAM. It should be understood,however, that the methods of providing rugged and/or hemispherical grainsilicon according to the present invention could be used in anyapplication or structure in which increased surface area in a layer ofconductive silicon would be useful.

Furthermore, the methods of the present invention are particularlywell-suited for providing rugged silicon on a surface of a semiconductorsubstrate or substrate assembly, referred to herein generally as“substrate,” used in forming integrated circuits, such as a siliconwafer, with or without layers or structures formed thereon. It is to beunderstood that the methods of the present invention are not limited todeposition on silicon wafers; rather, other types of wafers (e.g.,gallium arsenide, etc.) can be used as well. Also, the methods of thepresent invention can be used in connection with silicon-on-insulator orsilicon-on-sapphire technology. In addition, substrates other thansemiconductor substrates or substrate assemblies can be used inconnection with the present invention. These include, for example,fibers, wires, etc. If the substrate is a semiconductor substrate orsubstrate assembly, the rugged silicon can be formed directly on thelowest semiconductor surface of the substrate, or they can be formed onany variety of other layers or structures formed on the substrate.

FIG. 1 depicts a layer 10 of HSG silicon formed on a substrate 14. Thelayer 10 of HSG silicon has a roughened surface 12 that contributes tothe increased surface area desired in, for example capacitor structures.

Hemispherical grain silicon can be formed from a layer of in situ dopedamorphous silicon using a single temperature process according to thepresent invention in which a layer of doped amorphous silicon isdeposited on a substrate at a substantially constant depositiontemperature. The preferred temperature range lies in theamorphous-polysilicon transition zone, i.e., the range of temperaturesabove which substantially amorphous silicon would typically be depositedand below which substantially polycrystalline silicon would typically bedeposited. More specifically, the deposition temperature is preferablybetween about 560° C. to about 590° C., more preferably between about565° C. to about 575° C.

Although the deposition temperature is above typical amorphous silicondeposition temperatures, the formation of polysilicon can be reduced byincreasing the silicon deposition rate to the point at which thedeposition time for the desired thickness of silicon is below theincubation time needed for substantial polysilicon formation at thedeposition conditions (pressure, temperature, gas flow rate, etc.).

One method of increasing the silicon deposition rate is to increase theflow rate of the gas used to form the silicon layer. If silane is usedas the growth gas, it is preferably provided at a flow rate of about 50standard cubic centimeters per minute (sccm) or greater, more preferablyabout 100 sccm or greater, and even more preferably at about 200 sccm orgreater. By providing an increased flow rate of the growth gas, theformation of polysilicon can be reduced by increasing the overall rateof silicon deposition in spite of the relatively high depositiontemperatures. As a result, the time needed to deposit a layer of siliconof the desired thickness can be maintained below polysilicon incubationintervals.

Alternatively or in addition to increasing the flow rate of the growthgas, another technique to provide for amorphous silicon deposition is touse one or more growth gases that are more reactive than silane.Examples of more reactive gases include disilane and silicochloroform.The more reactive gases can be used alone, in combination with eachother, in combination with silane, or together in combination withsilane (i.e., a mixture of silane, disilane, and silicochloroform).

Yet another technique useful to provide for amorphous silicon depositionis to increase the pressure in the deposition chamber. This techniquecan be used alone or in combination with increased flow rates and/ormore reactive growth gases to provide for amorphous silicon formation.

Regardless of the technique or techniques used, the desired result inmethods according to the present invention is to limit or control theformation of polysilicon during the deposition of a substantiallyamorphous layer of in situ doped silicon on the substrate. Afterformation of the substantially amorphous in situ doped layer of silicon,the subsequent annealing step can take place at substantially the sametemperature at which the silicon was first deposited. Thecrystallization of the substantially amorphous layer of silicon takesplace after the pressure in the chamber has been reduced while thetemperature is maintained substantially constant.

It is theorized that the crystallization of the amorphous silicon duringthe annealing period results from spontaneous crystallization inside thelayer of in situ doped amorphous silicon as opposed to atom surfacediffusion (which is typically relied on in conventional approaches toproviding HSG silicon from amorphous silicon such as seeding).

One advantage of this single-temperature process is that the impact ofthe process used to obtain the desired conductive hemispherical grainsilicon on the thermal budget of the integrated circuit can be reducedbecause no subsequent high temperature anneal step is required to formthe hemispherical grain silicon. The thermal budget for fabrication ofan integrated circuit is that combination of maximum time andtemperature of heat treatments utilized in the fabrication of theintegrated circuit. An integrated circuit can only be subjected to alimited number of thermal steps for a limited amount of time before itselectrical performance is potentially detrimentally affected. Forexample, exceeding the thermal budget may also cause dopant gradients atjunctions between two regions in an integrated circuit to diffuse, suchthat the potential barrier between the two regions is altered.Furthermore, thermal steps often cause dopants to migrate into undesiredregions, altering device characteristics. Using the method of thepresent invention to obtain conductive hemispherical grain silicon canreduce the portion of the thermal budget expended to obtain the desiredrugged surfaces provided by hemispherical grain silicon.

FIG. 2 illustrates a time-temperature curve for one process according tothe present invention. In Zone I the process or deposition temperaturein the chemical vapor deposition chamber is increased until it lies withthe transition zone as described above. Typically this temperature isabout 560° to about 590° C. It is preferred that the silicon layerdeposited in Zone I is in situ doped amorphous silicon. By amorphous, itis meant that the layer is substantially amorphous, although smallamounts of crystallized silicon may be intermixed in the layer. Thedopant will typically be phosphorous (provided as PH₃), although anyother suitable dopants could be provided in place of, or in addition to,phosphorous.

As one example, the gases provided in Zone I could include silane,disilane, or a combination thereof in addition to PH₃ as the source ofthe dopant. These gases may or may not be diluted with one or moresuitable carrier gases as desired.

A potential additional step in this method involves a Zone II in whichthe dopant gas is eliminated to provide a cap layer of undoped orlightly doped amorphous silicon over the doped layer of silicon. Thestructure formed is depicted in FIG. 3 where a layer of doped amorphoussilicon 20 is located on substrate 14. The cap layer 22 of undoped orlightly doped amorphous silicon is provided over the layer 20 of dopedamorphous silicon. The cap layer 22 may enhance formation ofhemispherical grain silicon due to surface mobility enhancement.

In addition to surface mobility enhancement, the change in dopantconcentration between the doped amorphous layer 20 and undoped orlightly doped cap layer 22 results in a diffusion gradient between thelayers. It is theorized that diffusion, i.e., movement, of the dopantatoms from the doped layer 20 into the undoped or lightly doped caplayer 22 during crystallization may enhance the grain height in theresulting crystallized material because the dopant atoms are generallymoving or diffusing towards the exposed surface of the undoped orlightly doped cap layer 22.

The relative variations in dopant concentration between the doped layer20 and undoped or lightly doped cap layer 22 can be adjusted topotentially provide additional control over the grain height of theresulting hemispherical grain silicon layer. For example, a heavilydoped amorphous layer 20 and undoped amorphous cap layer 22 may providea more rugged surface than, for example, a heavily doped amorphous layer20 and lightly doped amorphous cap layer 22. The change in grain heightmay be, in part, attributed to the different diffusion gradients in thetwo examples. In other words, a higher diffusion gradient (caused by anincreased variation in dopant concentration in the amorphous silicon)will typically result in a more rugged surface while a lower diffusiongradient will typically result in a layer with reduced grain height(provided all other process parameters are relatively unchanged).

The optional cap layer 22 may also provide the advantage of reducingout-diffusion of the dopant from layer 20 during the subsequentannealing step during which the amorphous silicon layers 20 and 22 aretransformed into the desired HSG silicon layer 10 (see FIG. 1).

As indicated above, the method depicted in the graph of FIG. 2 includesan annealing step that occurs in Zone III. Unlike methods in whichannealing involves increasing the CVD chamber temperature, the methodaccording to the present invention involves maintaining the chambertemperature within the transition zone between amorphous and polysiliconformation.

To induce the crystallization necessary to form HSG silicon from theamorphous silicon layer or layers, the pressure in the CVD chamber isvaried during Zone III. The pressure in the chamber will typically beheld from about 200 mTorr to about 20 Torr during annealing. Bycontrolling the chamber pressure, the ruggedness of the HSG siliconlayer can be affected. Higher chamber pressures result in smoother HSGsilicon while lower pressures produce more pronounced surface features.In any event, control over the ruggedness of the surface features isaccomplished by chamber pressure control.

FIG. 4 depicts pressure in the CVD chamber during the process. As shown,pressure and temperature remain substantially constant during depositionof the doped amorphous silicon layer and undoped cap layer (if any). InZone III, however, pressure in the CVD chamber is reduced whiletemperature is held constant to produce the desired HSG silicon layer 10on substrate 14 (see FIG. 1).

Although the single temperature process described in this applicationgenerally involves holding the temperature at a substantially constantlevel during deposition and subsequent annealing, it may be possible insome situations to reduce the temperature during annealing (while alsoreducing pressure to initiate crystallization). Reducing temperatureduring annealing would further reduce the impact of the HSG siliconformation process on the thermal budget.

Turning now to FIGS. 5-7, an alternative method for providing HSGsilicon according to the present invention will be described. Like thefirst method, this method also begins with an initial step of depositinga first layer 32 of doped silicon on a substrate 30 (see FIG. 5) in achemical vapor deposition chamber. As depicted, this layer 32 isdiscontinuous, i.e., it does not completely cover the underlyingsubstrate 30. Preferably, the layer 32 forms substantially distinctislands of doped silicon on the surface of the substrate 30. It ispreferred that the discontinuous silicon layer 32 be substantiallyamorphous silicon as opposed to polysilicon.

To provide the discontinuous layer 32, it is preferred that thetemperature in the deposition chamber be held at about 600° C. or aboveto provide for discontinuous silicon growth in layer 32. Although thesetemperatures may typically be associated with the formation ofcrystalline polysilicon, layer 32 can be deposited as substantiallyamorphous silicon by maintaining the temperature for a relatively shortperiod of time, i.e., below polysilicon incubation intervals. Typically,the time during which the layer 32 is deposited should be limited toabout 3 minutes or less, more preferably about 1.5 minutes or less. Toensure that a sufficient amount of heavily doped amorphous silicon isdeposited in the substantially discontinuous areas making up layer 32,it may also be helpful to increase the flow rate of the source gasand/or use more reactive source gases as discussed with respect to thesingle temperature process described above.

To enhance the definition of the distinct areas or islands of layer 32,it may be advantageous to remove a portion of the layer 32 afterformation, particularly where the taller or thicker areas of the layer32 are connected by thinner areas of silicon layer. This step of removalcan be accomplished in a wet or dry process. It may be helpful toprovide the upper surface of the substrate 30 with a layer material suchas silicon nitride, etc. that can act as an etch stop for the etchingprocess used to partially remove the polysilicon layer 32. The removalstep should be controlled to leave the majority of thicker areas oflayer 32 on substrate 30, preferably as substantially distinct islands.

Layer 32 is formed relatively thin, preferably to a thickness of about1000 Angstroms or less, more preferably about 300 Angstroms or less.Because of the discontinuous nature of the layer 32, the thickness ismeasured as the average of the maximum height of each of thesubstantially discontinuous islands making up layer 32.

Layer 32 is also preferably heavily in situ doped for electricalconductivity. One dopant is phosphorous, although any suitable dopant orcombination of dopants could be used in layer 32. By heavily doped,layer 32 preferably contains a concentration of dopant of about 10²⁰atoms/cm³ or greater, more preferably about 10²¹ atoms/cm³ or greater.

After layer 32 has been formed and, if desired, a portion of the layerremoved, a substantially continuous second layer 34 of amorphous siliconis deposited on the first discontinuous layer 32 as well as the exposedportions of the underlying substrate 30 by chemical vapor deposition.This layer 34 can be either doped or undoped as desired. After layer 34has been deposited, both layers 32 and 34 can be annealed to furtherenhance the ruggedness of the resulting composite layer.

The change in dopant concentration between the doped discontinuoussilicon layer 32 and undoped or lightly doped continuous silicon layer34 results in a diffusion gradient between the layers. It is theorizedthat diffusion, i.e., movement, of the dopant atoms from the heavilydoped layer 32 into the undoped or lightly doped layer 34 duringcrystallization may enhance the grain height in the resultingcrystallized material because the dopant atoms are generally moving ordiffusing towards the exposed surface of the undoped or lightly dopedlayer 34.

The relative variations in dopant concentration between the doped layer32 and undoped or lightly doped layer 34 can be adjusted to potentiallyprovide additional control over the grain height of the resultinghemispherical grain silicon layer. For example, a heavily dopedamorphous layer 32 and undoped amorphous layer 34 may provide a morerugged surface than, for example, a heavily doped amorphous layer 32 andlightly doped amorphous layer 34. The change in grain height may be, inpart, attributed to the different diffusion gradients in the twoexamples. In other words, a higher diffusion gradient (caused by anincreased variation in dopant concentration in the amorphous silicon)will typically result in a more rugged surface while a lower diffusiongradient will typically result in a layer with reduced grain height(provided all other process parameters are relatively unchanged).

Some advantages to the method of providing HSG silicon as depicted inFIGS. 5 and 6 is that the resulting HSG silicon layer is typicallyhomogeneously doped, substantially continuous over the desired area,provides the desired increased surface area for enhancing capacitance(if used in a capacitor structure), and provides good step coverage overexisting structures on the substrate.

FIG. 7 is a graphical representation of the deposition temperature as afunction of time for providing the layers depicted in FIGS. 5 and 6. Asshown, the chamber or deposition temperature is held above thetransition zone for amorphous to polysilicon deposition. Preferably, thedeposition temperature during Zone I in FIG. 7 (in which layer 32 isformed) is about 600° C. or greater. After a sufficient amount ofsilicon has been deposited in Zone I, the temperature in the depositionchamber is reduced to levels at which the second layer 34 ofsubstantially continuous amorphous silicon is deposited on the firstlayer 32 and the exposed portions of the substrate 30 (see FIG. 6). Thatportion of the process is represented by Zone II in FIG. 7. Onepreferred deposition temperature during Zone II is about 550° C.

Zone III in FIG. 7 depicts the increase in temperature typically used toanneal the first and second layers 32 and 34. Some preferred annealtemperatures are about 560° C. to about 650° C. Preferably, the timespent in Zone III is about 10 minutes when the anneal temperature isabout 600° C. The annealing process results in the desired HSG siliconlayer. Alternatively, as described above, no annealing may be performedprovided that the discontinuous layer 34 is doped to provide the desiredelectrical conductivity.

The present invention also includes methods of providing rugged siliconsurfaces that may not result in the formation of hemispherical grainsilicon. This method is similar to that depicted in FIGS. 5 and 6.Referring now to FIG. 8, a first discontinuous layer 132 of silicon isformed in the same manner as described above for discontinuous layer 32.Discontinuous silicon layer 32 can be doped or undoped.

After formation of the discontinuous layer 132 (including any selectiveremoval of the layer 132 to enhance its discontinuous nature), a secondconformal layer 134 of doped silicon can be deposited on the first layer132 and any exposed portions of the substrate 130. Layer 134 ispreferably doped to provide for electrical conductivity required to forma capacitor plate. In this method, no annealing step is required becausethe rugged surface is provided by the conformal nature of layer 134 overthe rugged profile achieved with the discontinuous first layer 132. Ifno annealing occurs, hemispherical grain silicon may not be formed usinglayers 132 and 134. Alternatively, however, layers 132 and 134 can beconverted into hemispherical grain silicon through an annealing step ifdesired.

The methods of the present invention can be used to form conductiverugged silicon on any desired structure, but one method will be morespecifically described as used in the construction of a capacitorelectrode incorporating rugged silicon. Turning to FIG. 9, a substrate40 including a diffusion region 41 is provided. Access gates 42 arelocated above the diffusion region 41 and the distance between theaccess gates 42 is spanned by the diffusion region 41. The capacitorelectrode structure 43 connects to the diffusion region 41 betweenaccess gates 42. It is the surface of the upper portion of the capacitorelectrode structure 43 that includes the desired conductive ruggedsilicon surface.

Any of the methods according to the present invention described hereincan be used to provide the desired conductive rugged silicon surface oncapacitor electrode structure 43. After the conductive rugged silicon isformed on structure 43, a layer 44 of dielectric is deposited thereon,followed by formation of a second capacitor electrode 45 on thedielectric 44 to complete the capacitor.

EXAMPLES

The following nonlimiting examples are provided to illustrate methodsaccording to the present invention:

Example 1

A single temperature process for forming HSG silicon according to thepresent invention was performed as described below. A depositiontemperature of 565° C. was maintained throughout the process. Thesubstrate was a silicon wafer. The zones referred to correspond to thezones depicted in FIG. 2.

An amorphous layer of silicon was formed by providing a growth gas(SiH₄) to the CVD chamber at a rate of 200 sccm. A dopant gas comprising0.5% PH₃ in nitrogen was also supplied to the chamber at a rate of 10sccm to conductively dope the silicon. The pressure in the chamber wasmaintained at 200×10⁻³ Torr. These conditions were held for about 20minutes and resulted in the formation of a layer of amorphous siliconwith a thickness of about 500 Angstroms. The above conditions definedZone I as referred to in FIG. 2.

A cap layer of undoped amorphous silicon was formed over the dopedamorphous silicon under the following conditions (Zone II in FIG. 2): agrowth gas (SiH₄) was provided to the chamber at a rate of 200 sccm andthe pressure in the chamber was maintained at 200×10⁻³ Torr. Theseconditions were held for about 5 minutes to form a cap layer of undopedamorphous silicon with a thickness of about 200 Angstroms.

The two layers of amorphous silicon were then subjected to annealing inthe same CVD chamber under the following conditions (Zone III in FIG.2): a non-reactive gas (nitrogen) was provided to the chamber at a rateof 500 sccm and pressure in the chamber was raised to 300×10⁻³ Torr.These conditions were maintained for about 30 minutes and resulted inthe formation of HSG silicon.

Example 2

A layer of HSG silicon was provided by beginning with a discontinuouslayer of silicon according to the present invention. The substrate was asilicon wafer. The zones referred to correspond to the zones depicted inFIG. 7.

A discontinuous layer of doped silicon was formed during Zone I of theprocess depicted in FIG. 7 by providing a growth gas (SiH₄) to the CVDchamber at a rate of 200 sccm. A dopant gas comprising 0.5% PH₃ innitrogen was also supplied to the chamber at a rate of 10 sccm toconductively dope the discontinuous layer of silicon. The temperature inthe chamber was held at 600° C. and the pressure in the chamber wasmaintained at 200×10⁻³ Torr. These conditions were held for about 3minutes and resulted in the formation of a discontinuous layer of dopedsilicon with a thickness of about 500 Angstroms.

Following formation of the discontinuous silicon layer, the temperaturein the CVD chamber was reduced to 530° C. and the flow rate of thedopant gas was lowered to 5 sccm. Pressure in the chamber was maintainedat 200×10⁻³ Torr. These conditions were held for about 30 minutes toform a layer of doped amorphous silicon on the discontinuous layer, withthe thickness of the doped amorphous layer being about 300 Angstroms.This portion of the process is represented as Zone II in FIG. 7.

The two layers of silicon were then subjected to annealing in the sameCVD chamber under the following conditions (Zone III in FIG. 7): anon-reactive gas (nitrogen) was provided to the chamber at a flow rateof 500 sccm and pressure in the chamber was raised to 300×10⁻³ Torr. Thetemperature in the chamber was also increased to about 570° C. and theseconditions were maintained for about 30 minutes, resulting in theformation of conductive HSG silicon.

Although specific methods and examples have been illustrated anddescribed herein, it will be appreciated by those of ordinary skill inthe art that any arrangement that is calculated to achieve the samepurpose may be substituted for the specific methods and examplesdescribed. This application is intended to cover any adaptations orvariations of the present invention. Therefore, it is manifestlyintended that this invention be limited only by the claims and theequivalents thereof.

What is claimed is:
 1. A method of forming hemispherical grain silicon,comprising: locating a substrate within a chamber; forming an amorphoussilicon layer on the substrate at a deposition temperature and at afirst chamber pressure; and converting the amorphous silicon layer intohemispherical grain silicon by subjecting the amorphous silicon layer toa temperature no greater than the deposition temperature and to a secondchamber pressure different than the first chamber pressure.
 2. Themethod according to claim 1, wherein the second chamber pressure heldfrom about 200 mTorr to about 20 Torr.
 3. The method according to claim1, wherein the deposition temperature is about 560° C. to about 590° C.4. A method of forming hemispherical grain silicon on a substrate,comprising: forming an amorphous silicon layer on the substrate at asubstantially constant deposition temperature within a chamber, thechamber at a substantially constant first chamber pressure; andtransforming the amorphous silicon layer into hemispherical grainsilicon by subjecting the amorphous silicon layer to a temperature nogreater than the deposition temperature and to a second chamber pressuredifferent than the first chamber pressure.
 5. The method according toclaim 4, wherein forming the amorphous silicon layer comprises providinga growth gas to the chamber at a flow rate of about 50 standard cubiccentimeters per minute (sccm) or greater.
 6. The method according toclaim 4, wherein the deposition temperature is about 560° C. to about590° C.
 7. The method according to claim 6, wherein the depositiontemperature is about 565° C. to about 575° C.
 8. A method of forminghemispherical grain silicon, comprising: forming a first layer of insitu doped amorphous silicon on a substrate at a substantially constantdeposition temperature; forming a second layer of undoped or lightlydoped amorphous silicon on the first layer, the second layer beingformed at the deposition temperature within a chamber at a first chamberpressure; and converting the first layer and the second layer intohemispherical grain silicon by maintaining the deposition temperatureand subjecting the first and second layers to a second chamber pressurethat is different than the first chamber pressure.
 9. The methodaccording to claim 8, wherein the deposition temperature is about 560°C. to about 590° C.
 10. The method according to claim 8, wherein thesecond chamber pressure is between about 200 mTorr to about 20 Torr. 11.A method of forming hemispherical grain silicon, comprising: forming alayer of doped, substantially amorphous silicon on a substrate locatedwithin a chamber at a first chamber pressure, wherein the substrate,during formation of the layer, is at a substantially constant depositiontemperature that is in a range of temperatures above which substantiallyamorphous silicon would typically be formed and below whichsubstantially polycrystalline silicon would typically be formed; andexposing the layer of doped, substantially amorphous silicon to a secondchamber pressure that is different from the first chamber pressure, andto a temperature equal to or less than the deposition temperature. 12.The method according to claim 11, wherein the range of temperatures isfrom about 560° C. to about 590° C.
 13. The method according to claim11, wherein the second chamber pressure is about 200 mTorr to about 20Torr.
 14. A method of forming hemispherical grain silicon, comprising:forming a first layer of doped substantially amorphous silicon on asubstrate at a substantially constant deposition temperature, thedeposition temperature in a range of temperatures above whichsubstantially amorphous silicon would typically be formed and belowwhich substantially polycrystalline silicon would typically be formed;forming a second layer of undoped or lightly doped substantiallyamorphous silicon on the first layer, the second layer formed within achamber at a first chamber pressure; and exposing the first and secondlayers to a second chamber pressure that is different from the firstchamber pressure, and to a temperature equal to or less than thedeposition temperature.
 15. The method according to claim 14, whereinthe range of temperatures is from about 560° C. to about 590° C.
 16. Themethod according to claim 14, wherein the first layer is formed byproviding a growth gas to the chamber at a flow rate of about 50 sccm orgreater.
 17. The method according to claim 16, wherein the flow rate ofgrowth gas is about 100 sccm or greater.
 18. The method according toclaim 17, wherein the flow rate of growth gas is about 200 sccm orgreater.
 19. The method according to claim 16, wherein at least aportion of the growth gas comprises a gas selected from the groupconsisting of silane, disilane, silicochloroform, and combinationsthereof.
 20. The method according to claim 14, wherein the secondchamber pressure is about 200 mTorr to about 20 Torr.
 21. A method offorming hemispherical grain silicon, comprising: forming a first layerof doped substantially amorphous silicon on a substrate located within achamber, the first layer formed by providing a growth gas to the chamberat a flow rate of about 50 sccm or greater, wherein the substrate,during formation of the first layer, is heated to a depositiontemperature that is in a range of temperatures above which substantiallyamorphous silicon would typically be formed and below whichsubstantially polycrystalline silicon would typically be formed; forminga second layer of undoped or lightly doped substantially amorphoussilicon on the first layer, the second layer being formed at thedeposition temperature and at a first chamber pressure; and exposing thefirst layer and the second layer to a second chamber pressure that isdifferent from the first chamber pressure, while maintaining atemperature no greater than the deposition temperature.
 22. The methodaccording to claim 21, wherein the flow rate of growth gas is about 100sccm or greater.
 23. The method according to claim 22, wherein the flowrate of growth gas is about 200 sccm or greater.
 24. The methodaccording to claim 21, wherein the growth gas comprises disilane. 25.The method according to claim 21, wherein at least a portion of thegrowth gas comprises a gas that is more reactive than silane.
 26. Themethod according to claim 21, wherein at least a portion of the growthgas comprises a gas selected from the group consisting of silane,disilane, silicochloroform, and combinations thereof.
 27. The methodaccording to claim 21, wherein the second chamber pressure is about 200mTorr to about 20 Torr.